Dodging a ball approaching on a collision path: Effects of eccentricity and velocity

Animals generally seek to avoid potentially harmful collisions. To perform successful avoidance, actors must correctly perceive the approach of an obj ect and produce an appropriate motor response. Objects can approach from an y part of the visual field, but avoidance skills are particularly relevant when threatening approaches occur in peripheral vision. This type of behavi or has so far received little attention. Stoffregen and Riccio (1990) found that participants are sensitive to visually simulated impending collision at 0 or 90 degrees. However, motor behavior produced in response to a real object approaching at various angles of eccentricity and at various speeds has not been investigated. In this study, participants were asked to dodge a ball approaching at 0, 20 , 40, 60, or 80 degrees of eccentricity. The ball was travelling at a const ant speed of 1.0, 1.5, or 2.0 m/sec. Results showed that time to contact (T TC) at initiation of the avoidant response was similar for 0 and 20 degrees but increased from 20 to 80 degrees. Angle of approach had no effect on pa rticipants' movement velocity. Ball speed had an effect on both variables. TTC de creased and participants' movement velocity increased with eccentric ity. No interaction was observed between ball. speed and eccentricity. Thes e results show that a successful motor response to impending physical colli sion is possible across a wide range of approach eccentricities. It appears that the speed of the approach was accurarely perceived. The speed of avoi dant responses was consistent, suggesting that intensity coupling, that is, a coupling of movement velocity with stimulus speed, was not affected by t he eccentricity.